1. Field of the Invention
The present invention relates to a hollow, fluid conveying needle, and more particularly, concerns a needle cannula with an improved pointed end which is intended primarily for penetration of the skin of a patient.
2. Description of the Prior Art
When using a hollow needle cannula for the conveyance of fluid particularly through the skin of a patient, a number of significant factors must be considered in the design of such cannula. For instance, the needle cannula should be sufficiently rigid and stiff so that it can effectively penetrate the skin of the patient without breaking or bending to such a degree so as to occlude the fluid path. In this regard, such needle cannulae are primarily made of metal so as to impart these desired stiffness characteristics. In addition to surface lubricity of the needle and the sharpness of the point, the outside diameter of the needle and its wall thickness play a factor in the penetration of the skin and the discomfiture attendant with such penetration. It has been suggested that reduction in the outside diameter and the wall thickness of the needle will provide greater ease in penetration of the skin of the patient. However, there is usually a tradeoff in merely reducing the outside diameter of the needle in order to achieve this desired ease of penetration. This tradeoff generally involves a narrowing or constriction of the inside diameter of the needle along with the reduction of the outside diameter of the needle. As a result, the flow rate capability through the needle is impaired, especially if large flow rates or quantities of fluid are to be conveyed through the needle. Furthermore, merely reducing the wall thickness of the needle will compromise the stiffness characteristics of the needle so that there will be a greater tendency to bend or break during its use.
In U.S. Pat. No. 3,540,447, a spinal needle is disclosed in which the pointed end has a reduced diameter when compared to the remainder of the needle. It can be seen, however, that the inside lumen of this patented needle has a smaller cross-sectional dimension than the lumen in the enlarged portion of the needle. As a result, any fluid flowing through this patented needle will be subject to flow rate deviations through the narrow pointed end of the needle. Another patent which discloses a reduced diameter point on the needle is U.S. Pat. No. 3,216,616.
With the foregoing in mind, improvements are still being sought in the point end of a needle cannula which will overcome many of the deficiencies noted above.